Q. 1 - 17 due Thursday, March 3, 6:00 pm. Homework #4 Q. 1 - 17 due Thursday, March 3, 6:00 pm. Q. 18 - 21 due Wednesday, March 2, 2:30 pm. Q. 19, 20 & 21 are extra credit

Saturn’s moon Hyperion: odd surface with strange looking craters whose floors are covered with an unknown dark material. Hyperion is about 250 kilometers across, rotates chaotically, and has a density so low that it might house a vast system of caverns inside.

Emission line spectrum. A hot, low density gas emits light of only certain wavelengths, determined by the composition of the gas.

Absorption line spectrum. When light with a continuous spectrum passes through a cool gas, dark lines appear in the continuous spectrum at wavelengths determined by the composition of the absorbing gas.

Absorption Spectra If light shines through a gas, each element will absorb those photons whose energy match their electron energy levels. The resulting absorption line spectrum has all colors minus those that were absorbed. We can determine which elements are present in an object by identifying emission & absorption lines.

Red Blue

The interior of a star is hot and dense, producing a continuous spectrum. However, the light emerging from the interior of a star must pass through the star’s cooler atmosphere before we can see it. Photons at specific wavelengths are absorbed while passing through the relatively cool photospheric gas. As a result, we typically see an absorption spectrum when observing stars.

Molecules have rotational & vibrational energy levels. These levels are less energetic than electron energy levels. Therefore energy level transitions involve photons with less energy that visible photons. Energies correspond with photons in the infrared, microwave, and radio portion of the electromagnetic spectrum.

The Ring Nebula a “planetary nebula” Understanding the three types of spectra

A. The white dwarf star (a thermal radiator) in the center of the nebula. B. A distant star (that is much hotter than the gas) viewed through the cold gas expelled by the dying star. C. An empty, dark region of space. D. The diffuse gas expelled by the dying star seen against the dark background of space. E. What type of element(s) do you expect to see in some of these spectra? Why? What kind of spectrum is seen at each location depicted below? Explain.

The Doppler Shift: A shift in wavelength due to a wave emitter moving towards (shorter wavelength) or away (longer wavelength) from an observer.  v  c =

The Doppler Effect BLUESHIFT REDSHIFT 1. Light emitted from an object moving towards you will have its wavelength shortened. BLUESHIFT 2. Light emitted from an object moving away from you will have its wavelength lengthened. REDSHIFT 3. Light emitted from an object moving perpendicular to your line-of-sight will not change its wavelength.

Measuring Radial Velocity We can measure the Doppler shift of emission or absorption lines in the spectrum of an astronomical object. We can then calculate the velocity of the object in the direction either towards or away from Earth. (radial velocity)  v  c =

Measuring Rotational Velocity

If the wavelength of an electromagnetic wave increases, its velocity (red) Decreases (yellow) Increases (blue) Remains the same (green) Not enough information

If the wavelength of an electromagnetic wave increases, its velocity (red) Decreases (yellow) Increases (blue) Remains the same (green) Not enough information

If the wavelength of an electromagnetic wave increases, its frequency (red) Decreases (yellow) Increases (blue) Remains the same (green) Not enough information

If the wavelength of an electromagnetic wave increases, its frequency (red) Decreases (yellow) Increases (blue) Remains the same (green) Not enough information

If the wavelength of an electromagnetic wave increases, its energy (red) Decreases (yellow) Increases (blue) Remains the same (green) Not enough information

If the wavelength of an electromagnetic wave increases, its energy (red) Decreases (yellow) Increases (blue) Remains the same (green) Not enough information

Phases of Matter solid liquid gas plasma the phases solid liquid gas plasma depend on how tightly the atoms and/or molecules are bound to each other As temperature increases, these bonds are loosened:

Recall that temperature measures the average kinetic energy of particles (K.E. = ½ mv2). Faster particles can escape electrical bonds easier. At a given temperature, smaller mass particles will be moving faster than higher mass particles

Matter, Forces and Motion

Scalars and Vectors Scalar: a quantity described solely by its size (and units) Vector: a quantity described by its size AND direction

speed – rate at which an object moves [e.g., m/s]. A scalar quantity. velocity – an object’s speed AND direction, [e.g.,10 m/s east]. A vector quantity. acceleration – a change in an object’s velocity, i.e., a change in speed OR direction [m/s2]. A vector quantity.

Force, momentum, and acceleration are all vectors Momentum (p) – the mass of an object times its velocity (p=mv) Force (f) – anything that can cause a change in an object’s momentum As long as the object’s mass does not change, a force causes a change in velocity, or an acceleration (a) Force, momentum, and acceleration are all vectors

What is the natural state of motion?

Newton’s First Law of Motion A body in motion remains in motion and a body at rest remains at rest unless acted upon by an outside force. OR If the net force acting on an object is zero, then there is no change in the object’s motion.